As you know, Fedora 19 Alpha has been released. Installing LXDE on Fedora 19 is an easy task, all you have to do is:
$ sudo yum install @lxde-desktop
If you have KDM or GDM, just reboot and choose LXDE as default from the menu.
To set LXDE as default for LXDM, do this:
$ sudo su
# cd /etc/systemd/system; rm display-manager.service ;ln -s /usr/lib/systemd/system/lxdm.service display-manager.service
Now reboot and enjoy.